The debate’s moderator is well-known TV moderator Morteza Heidari, He also hosted the 2013 debates.

No woman has ever been allowed to run. 137 registered to run in the May vote, all were disqualified, including activist and editor Azam Taleghani.

Read our profile of Taleghani who has already been rejected three times:

The start of the debate has been delayed by 30 minutes. It will now begin at 4:30 p.m. local time, that's 12 p.m. GMT.

Farzan Sabet, a nuclear security fellow at Stanford University and managing editor of a website, IranPolitik.com, has a look at the three main candidates:

Ahead of the May 19 vote, Iran has blocked Instagram live video feature, the semi-official ILNA news agency reports. Iran's hard-line judiciary last week blocked calls on the highly popular messaging app Telegram.

All six candidates are sitting in a back room awaiting the start of the debate. Nervous?!

Here's a quick glimpse at the six candidates in today's debate. They are the last candidates standing after the Guardians Council reviewed around 1,600 applications -- reportedly including just a couple dozen serious aspirants -- for the ballot.

Profiles: Six Still Standing In Race For Iran's Presidency

The debates are key to building public interest in the vote. They’re held on Fridays -- the weekend in Iran --so that people have time to watch them. The first live televised debates were held in 2009, generating great interest among Iranians.

Candidates are on the stage, listening to the Koran reading. The debate will start any minute now.